The xterm_flag variable was initialized in setup_mc() but used
first time in init_key() and in tty_init() (in do_enter_ca_mode())
before setup_mc() call.
Now xterm initialized in early step of mc start up process and
xterm support and mouse are initialized in tty_init().
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>